Suspension architecture for a snowmobile

ABSTRACT

A rear suspension architecture is provided for coupled rear suspension systems.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/968,749 filed Dec. 15, 2010, which is a divisional of U.S.application Ser. No. 11/709,421, filed on Feb. 22, 2007, which claimsthe benefit of U.S. Provisional Application Ser. No. 60/775,997 filedFeb. 24, 2006, the disclosures of which are fully incorporated herein byreference.

FIELD OF THE INVENTION

The invention relates generally to the architecture for a snowmobilesuspension system.

BACKGROUND AND SUMMARY

Most snowmobiles include a chassis, an engine, a transmission, andendless belt assembly designed to contact the ground and propel thesnowmobile. Typical snowmobiles also include a pair of front skissupport by a front suspension system. The endless belt assemblygenerally includes a rear suspension system designed to help the beltassembly maintain contact with the ground when riding over uneventerrain and provide the rider with a comfortable ride.

Generally, there are two types of snowmobile rear suspensions in thesnowmobile industry: coupled and uncoupled. The term “coupled” isgenerally given to suspensions that have dependant kinematicsfront-to-rear and/or rear-to-front relative to the lower rails of therear suspension. A suspension is coupled rear-to-front when the frontportion of the lower rails is deflected vertically and the rear portionof the lower rails is forced to move vertically to some degree. Asuspension is coupled rear-to-front when the rear portion of the lowerrails is deflected vertically and the front portion of the lower railsis forced to move vertically to some degree. An uncoupled rearsuspension is generally independent front-to-rear and rear-to-frontrelative to the lower rails of the rear suspension. A verticaldeflection of the front portion of the suspension causes little to novertical deflection of the rear portion of the suspension and viceversa.

Coupled suspensions differ from uncoupled suspension in at least twoareas. There is a distinct stiffness or rate of deflection of the rearsuspension per pound of force applied to the rear suspension for boththe front and rear portion of the rear suspension. A coupled suspensioncombines the rates of both the front and rear portions of the rearsuspension so the overall rate becomes higher than rate that may beachieved with an uncoupled rear suspension. Second, a coupled rearsuspension may be used to control weight transfer to the rear suspensionduring acceleration of the snowmobile.

One embodiment of the present invention includes a snowmobile comprisinga chassis, a motor supported by the chassis, and an endless beltassembly including a belt and a coupled suspension, the coupledsuspension including a lower rail, a front and rear control arm, a firstand second bump stop, and a coupling member positioned between the firstand second bump stops, the front control arm adapted to operably connectthe lower rail to the chassis, the rear control arm adapted to operablyconnect the coupling member to the chassis, the first bump stopsupported by the lower rail at a first position, the second bump stopsupported by the lower rail at a second position, the coupling memberpivotally supported to the lower rail, the coupling member beingmoveable between the first bump stop and the second bump stop, thecoupling member configured to exert a horizontal and vertical force onthe second bump stop, the vertical force being greater than thehorizontal force.

Another embodiment of the present invention includes a snowmobile havinga coupled suspension, the snowmobile comprising a chassis having a frontand rear end, a lower rail, a front control arm positioned adjacent tothe chassis front end, the front control arm pivotally interconnectingthe chassis and the lower rail, a rear inverted control linkinterconnected to the lower rail, a rear control arm positioned adjacentto the chassis rear end and pivotally interconnected to the chassis andthe rear inverted control link, the rear control arm interconnected tothe rear inverted control link at a position below the interconnectionbetween the rear inverted control arm and the lower rail, and a couplingmember providing a controlled degree of freedom of movement between thecoupling member and the rear control arm, until coupling between therear control arm and the lower rail occurs.

Another embodiment of the present invention includes a snowmobilecomprising a chassis having a front and rear end, a lower rail, a frontcontrol arm defining a first length extending between first and secondspaced-apart ends, the front control arm positioned adjacent to thechassis front end, the front control arm pivotally coupled to thechassis on the first end and pivotally coupled to the lower rail on thesecond end, a rear control arm positioned adjacent to the chassis rearend and pivotally interconnected to the chassis and lower rail, alinkage assembly supported by the front control arm at a first positionbetween the first and second ends of the front control arm, the firstposition being spaced-apart from the second end of the front control armby at least a first distance, the first distance being defined byone-quarter of the length of the front control arm, and a shock absorberand pull rod each including first and second spaced-apart ends, thefirst ends interconnected to the rear control arm, the second endsoperably coupled to the linkage assembly.

Another embodiment of the present invention includes a snowmobilecomprising a chassis having a front and rear end, a lower rail havingfront and rear ends, and an endless belt assembly including a belt, afront control arm, a rear control arm, a coupling member, and a belttensioning system, the front control arm positioned adjacent to thechassis front end and adapted to pivotally interconnect the chassis andthe lower rail, the rear control arm positioned adjacent to the chassisrear end and adapted to pivotally interconnect the chassis and one ofthe coupling member and the lower rail, the coupling member providing acontrolled degree of freedom of movement between the coupling member andthe rear control arm, the belt tensioning system configured to maintainan appropriate belt tension during movement between the chassis andlower rail.

In yet another embodiment, a snowmobile having a coupled suspensioncomprises a chassis, at least one lower rail, at least one front controlarm pivotally coupled to the chassis at a first end and pivotallycoupled to the lower rail on a second end, a rear control arm positionedadjacent to the chassis rear end and pivotally interconnected to thechassis and lower rail, a front linkage assembly supported by the frontcontrol arm, a rear linkage assembly supported by the rear control arm;a tension rod extending between the front and rear linkage, an LFEoperatively connected between the front linkage assembly and the rearlinkage assembly, and extending along a longitudinal line of action(LOA), where the LFE front pivot point and a front pivot point of thetension rod being substantially along the LOA, and being spaced apartfrom each other.

The above mentioned and other features of this invention, and the mannerof attaining them, will become more apparent and the invention itselfwill be better understood by reference to the following description ofembodiments of the invention taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a profile view of one embodiment of a snowmobile;

FIG. 2 is a profile view of the endless belt assembly of the snowmobileshown in FIG. 1;

FIG. 3 is a top view of the coupled rear suspension system of theendless belt assembly shown in FIG. 2;

FIG. 4 is an elevated, perspective view of the coupled rear suspensionsystem shown in FIG. 3;

FIG. 5 is a cross-sectional view of the coupled rear suspension systemshown in FIG. 4;

FIG. 6 is a partial, exploded view of the front portion of the coupledrear suspension system shown in FIGS. 3-5;

FIG. 7 is a perspective view of the rear portion of the coupled rearsuspension system shown in FIGS. 3-6;

FIG. 8 is a perspective view of components of the rear portion of thecoupled rear suspension system shown in FIG. 7;

FIG. 9 is a partial, exploded view of the rear portion of the coupledrear suspension system shown in FIGS. 3-8;

FIG. 10 is a profile view of the rear portion of the coupled rearsuspension system shown in FIG. 9, the rear suspension is shown in afirst position in solid lines and a second position shown in phantom;

FIG. 11 is a profile view of another embodiment of a snowmobile having acoupled rear suspension;

FIG. 12 is a profile view of the endless belt assembly of the snowmobileshown in FIG. 11;

FIG. 13 is a top view of the coupled rear suspension system of theendless belt assembly shown in FIG. 12;

FIG. 14 is an elevated, perspective view of the coupled rear suspensionsystem shown in FIG. 13;

FIG. 15 is a cross-sectional view of the of coupled rear suspensionsystem shown in FIG. 14;

FIG. 16 is a partial, exploded view of the front portion of the coupledrear suspension system shown in FIGS. 13-15;

FIG. 17 is a perspective view of the rear portion of the coupled rearsuspension system shown in FIGS. 13-16;

FIG. 18 is a perspective view of components of the rear portion of thecoupled rear suspension system shown in FIG. 17;

FIG. 19 is a partial exploded view of the rear portion of the coupledrear suspension system shown in FIGS. 13-18;

FIG. 20 is a profile view of the rear portion of the coupled rearsuspension system shown in FIG. 19, the rear suspension is shown in afirst position in solid lines and a second position shown in phantom;

FIG. 21 is a partial, perspective view of the belt tensioning assemblyof the coupled rear suspension system shown in FIGS. 11-20;

FIG. 22 is a partial, exploded view of the belt tensioning assemblyshown in FIG. 21;

FIG. 23 is a cross-sectional view of the belt tensioning assembly shownin FIGS. 21 and 22;

FIG. 24 shows an alternative front shock mount assembly;

FIG. 25 is an enlarged view of the mount shown in FIG. 24;

FIG. 26 is an exploded view of the shock mount assembly of FIG. 24;

FIG. 27 is a side view of the shock mount assembly of FIG. 25 at fullrebound;

FIG. 28 is a side view similar to that of FIG. 27 at full jounce;

FIG. 29 shows the front load case curve for three comparativesuspensions; and

FIG. 30 shows the rear load case curve for three comparativesuspensions.

Corresponding reference characters indicate corresponding partsthroughout the several views. Although the drawings representembodiments of the present invention, the drawings are not necessarilyto scale and certain features may be exaggerated in order to betterillustrate and explain the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The embodiments disclosed below are not intended to be exhaustive or tolimit the invention to the precise forms disclosed in the followingdetailed description. Rather, the embodiments are chosen and describedso that others skilled in the art may utilize their teachings. Forexample, while the following description refers primarily to a rearsuspension system for a snowmobile, it should be understood that theprinciples of the invention apply equally to other suspension systems.While the present invention primarily involves a snowmobile, it shouldbe understood, however, that the invention may have application to othertypes of vehicles such as all-terrain vehicles, motorcycles, watercraft,utility vehicles, scooters, and mopeds.

Referring to FIG. 1, one embodiment of a snowmobile 10 is shown.Snowmobile 10 includes a chassis 12, an endless belt assembly 14, and apair of front skis 20. Snowmobile 10 also includes a front-end 16 and arear-end 18.\

Referring now to FIGS. 2-4, endless belt assembly 14 includes a coupledrear suspension system 22 and a belt 24. Belt 24 extends around poweredroller 25 and idler rollers 26 which are mounted at various locations onsuspension system 22. Roller 25 is powered by an engine (not shown) andtransmission (not shown) of snowmobile 10. In operation roller 25rotates about its central axis to move belt 24 around endless beltassembly 14 to propel snowmobile 10. Coupled rear suspension system 22includes a pair of spaced-apart lower rails 28, a pair of front controlarms 30, a pair of rear control arms 32, a coupling member 34, and abelt tensioning assembly 36. Front control arms 30 are coupled togetheron an upper end by cross shaft 42. Cross shaft 42 couples to chassis 12of snowmobile 10. Similarly, rear control arms 32 are coupled togetherby cross shaft 44 which is coupled to chassis 12 of snowmobile 10.Together, chassis 12, front control arms 30, rear control arms 32, andlower rails 28 form a four-bar linkage. Front control arms 30 arepivotally coupled to lower rails 28 at pivot points 43. Rear links 32are coupled on their lower end to cross shaft 35 (FIG. 4). Cross shaft35 is pivotally coupled to coupling member 34 by fastener 39. Couplingmember 34 is pivotally coupled to lower rails 28 by fastener 79 (FIG.2). Coupling member 34 is described in more detail below.

Coupled suspension system 22 also includes a shock absorber 38 and pullrods 40 which are coupled between front control arms 30 and cross shaft44. The upper end of shock absorber 38 and pull rods 40 is coupled to apair of plates 46 which are coupled to cross shafts 44 and 45. Plates 46are rigidly coupled to cross shafts 44 and 45 to interconnect shockabsorber 38 and pulls rods 40 with rear control arms 32. The lower endsof shock absorber 38 and pull rods 40 are coupled to a linkage assembly47 including link 48. Pull rods 40 accelerate the stroke of shockabsorber 38 when coupled suspension system 22 is compressed. Link 42behaves as a bell crank.

Referring now to FIGS. 5 and 6, coupling link 48 is pivotally coupled onan upper end to bracket 50 which is mounted on cross shaft 52. Crossshaft 52 extends between front control arms 30 to provide strength andmaintain front control arms 30 in a parallel relationship. Link 48 ispivotally coupled to bracket 50 at upper end 54 of link 48. Shockabsorber 38 is coupled to link 48 at lower end 56 of link 48. Pull rods40 are coupled to link 48 at pivot point 58, which is positioned betweenupper end 54 and lower end 56 of link 48. Shock absorber 38 and pullrods 40 are operatively coupled to front links 30 by link 48 and bracket50. In this embodiment, bracket 50 is positioned about two-thirds of thelength of front links 30 away from lower pivot point 43. In otherembodiments, bracket 50 may be coupled to front links 30 at any positionbetween lower pivot point 43 and cross shaft 42. However, in thepreferred embodiment, bracket 50 is preferably coupled to front links 30at a position spaced-apart from lower pivot points 43 by at leastone-quarter of the length of front links 30.

Referring now to FIGS. 5-10, coupling member 34 is described. Rearcontrol arms 32 are coupled together on their lower end by cross shaft35. Cross shaft 35 is pivotally coupled between vertical plates 61 ofcoupling member 34 by bushing 37 and fastener 39. Vertical plates 61 ofcoupling member 34 are rigidly coupled together by cross shafts 66 and68. In this embodiment, vertical plates 61 are substantiallytriangularly shaped, however any suitable shape may be used. Bushing 78and fastener 79 extend through cross shaft 68 and apertures in lowerrails 28 to pivotally couple coupling member 34 between lower rails 28.Vertical plates 61 of coupling member 34 each include a back plate 62and a lower plate 64.

Suspension system 22 also includes a pair of bump stops 72 positioned oncross shaft 70 (FIG. 7) which is coupled between lower rails 28. Crossshaft 70 is coupled to lower rails 28 by fasteners 71. A second pair ofbump stops 76 (FIG. 10) is positioned on cross shaft 74. Cross shaft 74is coupled between lower rails 28 by fasteners 77 (FIG. 9). In thisembodiment, second pair of bump stops 76 is positioned substantiallybelow first pair of bump stops 72, as will be described further herein.

As shown in FIG. 10, coupling member 34 rotates about an axis defined byfastener 79. The range of motion or degrees of freedom of movement ofcoupling member 34 is limited by bump stops 72 and 76. When endless beltassembly encounters a bump or sudden change in elevation, couplingmember 34 rotates about fastener 79 and moves from a first position(shown in solid lines) in which lower plates 64 abut bump stops 76 to asecond position (shown in phantom) in which back plates 62 abut bumpstops 72. When coupling member 34 is in the first position, lower plates64 exert both a horizontal and vertical force on bump stops 76, howeverthe vertical force is greater than the horizontal force. It should beunderstood that lower plates 64 may be constructed to any suitablelength, however lengthening lower plates 64 and moving bump stops 76away from the axis defined by fastener 79 effectively lengthens a momentarm defined by lower plates 64 and reduces the contact force betweenlower plates 64 and bump stops 76.

During movement of coupling member 34 from the first position to thesecond position, the angle between rear control arms 32 and lower rails28 decreases and the effective length of lower rails 28 is lengthenedrelative to the four-bar orientation of chassis 12, lower rails 28,front control arms 30, and rear control arms 32. The effect oflengthening the lower rails 28 during a sudden change in elevation orjounce stiffens suspension system 22 and helps endless belt assembly 14maintain contact with the ground during jounce and weight transfercaused by acceleration.

Referring back to FIGS. 8 and 9, belt tensioning assembly 36 includes apair of extendable links 84 including first ends 86 and second ends 88.Links 84 may be extended or retracted to adjust the tension of belt 24.First ends 86 are pivotally coupled to coupling member 34. Couplingmember 34 includes a cross shaft 66 coupled between vertical plates 61.Bushing 80 extends through cross shaft 66 and apertures 82 in lowerrails 28. In this embodiment, apertures 82 are profiled as slightlyelongated slots, however any suitably shaped aperture may be used. Firstends 86 of links 84 are coupled to the ends of bushing 88 by fasteners87.

Referring now to FIG. 3, the second ends 88 of links 84 are coupled tocross shaft 91. Cross shaft 91 extends through apertures 90 in lowerrails 28 and supports idler rollers 26 (FIG. 4). Idler rollers 26support belt 24 and rotate about cross shaft 91. Links 84 translate themovement of coupling member 34 to cross shaft 91 to adjust the tensionof belt 24 during movement of suspension system 22. As coupling member34 moves between the first and second positions, as discussed above,links 84 move cross shaft 91 and idler rollers 26 frontward or rearwardto maintain the appropriate tension of belt 24.

Referring now to FIG. 11, another embodiment of a snowmobile 110 isshown. Snowmobile 110 includes a chassis 112, an endless belt assembly114, and a pair of front skis 120. Snowmobile 110 also includes afront-end 116 and a rear-end 118. Snowmobile 110 is similar tosnowmobile 10 shown in FIG. 1 with the exception of endless beltassembly 114, which is explained below.

Referring now to FIGS. 12-14, endless belt assembly 114 includes acoupled rear suspension system 122 and a belt 124. Belt 124 extendsaround powered roller 125 and idler rollers 126 which are mounted atvarious locations on suspension system 122. Similar to roller 25,discussed above, roller 125 is powered by an engine (not shown) andtransmission (not shown) of snowmobile 110. In operation roller 125rotates about its central axis to move belt 124 around endless beltassembly 114 to propel snowmobile 110.

Suspension system 122 includes a pair of spaced part lower rails 128, apair of front control arms 130, a pair of rear control arms 132, acoupling member 134, and a belt tensioning assembly 136. In thisembodiment, front control arms 130 include upper and lower portions 129and 131, respectively. Each upper portion 129 is interconnected witheach lower portion 131 by cross shaft 152 (FIG. 14). Each front controlarm 130 also includes a bracing member 133 extending between upperportion 129 and lower portion 131 to provide added strength. Frontcontrol arms 130 are coupled together on an upper end by cross shaft142. Cross shaft 142 couples to chassis 112 of snowmobile 110. Similarlyrear control arms 132 are coupled together by cross shaft 144 which iscoupled to chassis 112 of snowmobile 110. Rear control arms 132 includebracing members 127 which couple to rear control arms 132 on a lower endand couple to cross shaft 144 on an upper end. When suspension system122 is in the coupled state, chassis 112, front control arms 130, rearcontrol arms 132, and lower rails 128 form a four-bar linkage. Frontcontrol arms 130 are pivotally coupled to lower rails 128 at lower pivotpoints 143. Rear control arms 132 are coupled to cross shaft 135 (FIG.15). Cross shaft 135 is coupled to inverted links 160 by bushing 178 andfastener 180. Coupling member 134 is pivotally coupled to lower rails128 by bushing 174 and fastener 176 which extend through cross shaft168. Coupling member 134 is described in more detail below.

Referring now to FIGS. 15 and 16, coupled rear suspension system 122also includes a shock absorber 138 and pull rods 140 which are coupledbetween front control arms 130 and cross shaft 144. The upper end ofshock absorber 138 and pull rods 140 is coupled to a pair of plates 146which are coupled to cross shaft 144. Plates 146 are rigidly coupled tocross shaft 144 to interconnect shock absorber 138 and pulls rods 140with rear control arms 132. The lower ends of shock absorber 138 andpull rods 140 are coupled to linkage 147 which includes link 150. Pullrods 140 increase the rate of compression of shock absorber 138 whencoupled rear suspension system 122 is compressed. Pull rods 140 andshock absorber 138 function in the same manner discussed above in thefirst embodiment, however, in this embodiment the lower ends of pullrods 140 and the lower end of shock absorber 138 are mounted coaxiallyon link 150.

Link 150 is pivotally coupled on an upper end to cross shaft 152. Crossshaft 152 is coupled to front control arms 130. Bushing 157 extendsthrough cross shaft 152 and link 150 and receives fasteners 159 topivotally couple link 150 to front control arms 132. Cross shaft 152also provides strength and maintains front control arms 130 in aparallel relationship. In this embodiment, link 150 is spaced-apart fromlower pivot points 143 by a distance equal to about one-half of thedistance between cross shaft 144 and lower pivot points 143. In otherembodiments, link 150 may be coupled to front links 130 at any positionbetween lower pivot points 143 and cross shaft 142. However, in thepreferred embodiment, link 150 is preferably coupled to front links 130at a position at least one-quarter of the distance between cross shaft142 and lower pivot points 143 above lower pivot points 143.

Referring now to FIGS. 15 and 17-20, coupling member 134 is described.Rear control arms 132 are coupled together on their lower end by crossshaft 135. Cross shaft 135 is pivotally coupled between inverted links160 of coupling member 134 by bushing 178 and fastener 180. Couplingplates 161 of coupling member 134 are coupled together by cross shaft168 and fasteners 177. In this embodiment coupling plates 161 have asemi-circular top profile, however any suitable shape may be used.Coupling plates 161 each include a slot 171 positioned coaxial to oneanother. Stops 162 and 164 are positioned between coupling plates 161and are secured by fasteners 177. As discussed above, bushing 174 andfastener 176 extend through cross shaft 168 and apertures in lower rails128 to pivotally couple coupling member 134 between lower rails 128.Stops 162 and 164 may be constructed of metal, rubber, plastic, or anysuitable substance.

As discussed above, the lower end of rear control arms 132 is couple tocross shaft 135. Fastener 180 extends though apertures in the lower endof inverted links 160 and bushing 178, which is positioned in crossshaft 135, to operably couple rear control arms 132 to coupling member134. Cross shaft 166 is coupled between rear control arms 132 andextends through slots 171 in inverted links 160 in coupling member 134.

As shown in FIG. 20, rear control arms 132 rotate about an axis definedby fastener 180. In this embodiment, the position of the pivot point ofrear control arms 132, the axis defined by fastener 180, is locatedbelow the location of the coupling point, cross shaft 166, of rearcontrol arms 132. The range of motion or degrees of freedom of movementof rear control arms 132 is limited by stops 162 and 164 and/or slots171 of coupling member 134. When endless belt assembly 114 encounters abump or sudden change in elevation, rear control arms 132 rotate aboutan axis defined by fastener 180 and moves from a first position (shownin solid lines) in which cross shaft 166 abuts stop 162 to a secondposition (shown in phantom) in which cross shaft 166 abuts stop 164.During this movement, rear suspension 122 is in an “uncoupled” state.

When cross shaft 166 abuts stop 162 and rear control arms 132 continueto move toward lower rails 128, coupling member 134 is forced to rotatedownward about an axis defined by fastener 176. When this occurs,suspension 122 returns to a “coupled” state. Similarly, when cross shaft166 abuts stop 166 and rear control arms 132 continues to move away fromlower rails 128, coupling member 134 is forced to rotate upward about anaxis defined by faster 176. When this occurs, suspension system 122 onceagain returns to a “coupled” state. The inverted pivot orientation ofcoupling member 134 and rear control arms 132 decreases and theeffective length of rear control arms 132 relative to the four-barorientation of chassis 112, lower rails 128, front control arms 130, andrear control arms 132. The effect of shortening rear control arms 130during a sudden change in elevation or jounce stiffens suspension system122 and helps endless belt assembly 114 maintain contact with the groundduring jounce and/or weight transfer caused by acceleration. In otherembodiments (not shown), coupling member 134 may include multiple bumpstops or may be constructed to form a slotted link to limit the degreeof freedom between coupling member 134 and rear control arms 132.

Referring now to FIGS. 18-23, belt tensioning assembly 136 is shown.Belt tensioning assembly 136 is similar to belt tensioning assembly 36described above and shown in FIGS. 1-10. Belt tensioning assembly 136includes a pair of extendable links 184 including first ends 186 andsecond ends 188. Links 184 may be extended or refracted to adjust thetension of belt 124. First ends 186 are pivotally coupled to invertedlinks 160 of coupling member 134 by cross shaft 170. Cross shaft 170extends through slots 172 in lower rails 128, apertures in invertedlinks 160, and first ends 186 of links 184. Fasteners 173 are receivedin cross shaft 170 to secure it in slots 172. In this embodiment, slots172 are elongated semi-circular slots, however any suitably shapedaperture may be used.

Second ends 188 of links 184 are supported by cross shafts 191. Crossshaft 191 extends into bushings 198. Bushings 198 interact withapertures 190 in lower rails 28 and slide blocks 194. Slide blocks 194are coupled to lower rails 128 and are positioned in apertures 190.Spacers 200 and bushings 202 are positioned between slide blocks 194 andidler rollers 126. Bushing 196 extends through idler wheels 126,bushings 202, spacers 200, slide blocks 194, bushings 198, crossbar 191,and second ends 188 of links 184. Fasteners 204 are received by bushing196 to secure the assembly. Idler rollers 126 support belt 124 androtate about bushing 196. Links 184 translate the movement of couplingmember 134 to bushing 196 to adjust the tension of belt 124 duringmovement of suspension system 122. As coupling member 134 moves betweenthe first and second positions, as discussed above, links 184 movebushing 196 and idler rollers 126 fore and aft along a longitudinal axisdefined by lower rails 128 to maintain the appropriate tension of belt124.

Referring now to FIGS. 24-26, a snowmobile suspension is described witha coupling member 234 similar in nature to coupling member 134 (FIG.14), yet with a different mounting system at the front end of shockabsorber 238. This system generally includes shock absorber or LFE 238and pull rods 240 which are coupled between front control arms 230 andcross shaft 244 (FIG. 26). The upper end of shock absorber 238 and pullrods 240 are coupled to a pair of plates 246 which are coupled to crossshaft 244. Plates 246 are rigidly coupled to cross shaft 244 tointerconnect shock absorber 238 and pulls rods 240 with rear links 227.As best shown in FIG. 25, the lower end of shock absorber 238 and pullrods 240 are coupled to linkage 247 which, includes links 250. Linkage247 in turn is pivotally attached to cross shaft 252 by way of pivotbracket 300. Pull rods 240 increase the rate of compression of shockabsorber 238 when coupled rear suspension system is compressed. Pullrods 240 and shock absorber 238 function in the same manner discussedabove in the first embodiment, however, in this embodiment the lowerends of pull rods 240 and the lower end of shock absorber 238 aremounted in line.

With respect to FIG. 26, link 250 is pivotally coupled on an upper endto bracket 300. Cross shaft 252 is coupled to front control arms 230.Bushing 257 extends through link 250 and receives a fastener 259 topivotally couple link 250 to front control arms 230. Cross shaft 252also provides strength and maintains front control arms 230 in aparallel relationship. In this embodiment, lower end of shock absorber238 is attached to link 250 by way of a C-shaped link 320. Lower end ofshock absorber 238 includes a mounting arm 322 having mountingapertures. C-shaped link includes spaced apart C-shaped plates 324,where fasteners 326 may be received therethrough for fastening theC-shaped link to the mounting arm 322. Link 320 has an opening 330 witha pivot opening 332 opposite thereto.

Link 250 is somewhat triangular, and acts as a bell-crank, having apivot stub shaft 336 at one corner and apertures 338 at another. Opening330 can “wrap around” stub shaft 336, intermediate links 250 (see FIGS.2-5) with opening 332 aligned with opening 338. Thus a fastener 340 canbe received through opening 338; through sleeve 342 and opening 332, andthrough the opposite side of the link 250.

With the above described geometry, a progressive rate suspension isachieved that has the best behaviors of both the coaxial (FIG. 16embodiment) and an offset design (FIG. 5 embodiment). At full rebound,the system acts similar to a coaxial design because the tension rodpivot is on or near the shock absorber line of action (LOA), as bestshown in FIG. 27. As shown, the pivot point of the tension rod 240 (leftend as viewed in FIG. 27) is approximately 0.26 inches from the LOA, andwould preferably be within 0.75 inches, and more preferably within 0.50inches. At full jounce, the bell crank, formed by plates 246, rotates sothat the tension rod pivot is above the pivot of the shock absorber, asbest shown in FIG. 28.

As also shown in the attached curves of FIGS. 29, 30, one can see thatthe suspension of FIGS. 24-26 is optimized. The front/rear bias isimproved by lowering the front rate, but yet the front rate ismaintained with the same basic shape. With respect to the rear loadcase,a progressive rate is created.

While this invention has been described as having an exemplary design,the present invention may be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains.

1. A snowmobile having a coupled suspension, the snowmobile comprising:a chassis having a front and rear end; a lower rail; a front control armpositioned adjacent to the chassis front end, the front control armpivotally interconnecting the chassis and the lower rail; a rearinverted control link interconnected to the lower rail; a rear controlarm positioned adjacent to the chassis rear end and pivotallyinterconnected to the chassis and the rear inverted control link, therear control arm interconnected to the rear inverted control link at aposition below the interconnection between the rear inverted control armand the lower rail; and a coupling member providing a controlled degreeof freedom of movement between the coupling member and the rear controlarm, until coupling between the rear control arm and the lower railoccurs.
 2. The snowmobile of claim 1, wherein the snowmobile includes apair of spaced-apart lower rails.
 3. The snowmobile of claim 2, whereinthe snowmobile includes another front and rear control arm and anotherrear inverted control link to define a pair of front and rear controlarms and a pair of rear inverted control links.
 4. The snowmobile ofclaim 3, wherein the coupling member is positioned between thespaced-apart lower rails.
 5. The snowmobile of claim 1 wherein thecoupling member includes a housing including an opening extendingbetween a front and rear bump stop, the bump stops configured to limitthe degree of freedom of movement of the rear control arm and the lowerrail.
 6. The snowmobile of claim 5, further comprising a cross shaftsupported by the rear control arm, the cross shaft adapted to bepositioned and move within the opening in the housing of the couplingmember.